Rotary tube-furnace for producing continuously calcium cyanamid.



. J. H. LIDHOLM.

- ROTARYTUBE FURNACE FOR PRODUCING C-ONTINUOUSLY CALCIUM CYANAMIDAPPLICATION FILED FEB.14. 1914.

1,191,804. Patented July 18, 1916;

Unrrnn s rarns PM 'JoHAii' HJALMAR Lrnrromu, or LCfiDOlST, ENGLAND.

oFFICE Specification-of Letters-Patent. Patented July i8,1916.

Application filedcFebruary 14,1914. sen iiol 'eisxss.

T c all whom z'zfk-m ay concern:

Be it known that I, -JOHAN HJALMAR ,LIDHOLM, a citizen of the Kingdom ofSweden, residing at London, England, Great .Britain, have invented newand use: ful Improvements in Rotary Tube-Furnaces v for ProducingContinuously Calcium Cy- =anamid, of which the following is a speciicyanainid; as far as known'said attempts ,have not. however, beensuccessful, no doubt,

fication.

As? is well known, calciumcyanamid is produced by heating calcium carbid'in an atmosphere of nitrogen to a temperature ,of about 1100 C., thenitrogen thereby being absorbed directly, while carbon is separated.Said .reaction is usuallyperformed in small retort furnaces heatedelectrically, and the reaction-1s hours.

completed after about 30 t to preheat th of the zone, of reaction may betransported the temperature. of reaction.

The invention as illustrated on the. ac}

' companying drawing showing a vertical lonorder to be able to uselarger'units of furnaces and to ,attain a shorterjtime of reaction;attempts have been made 'tofigse rotary tubefurnaces for producingcalcium depending upon the ditficulties, on the one side, in heating thecalcium ca bidin such a furnace to the temperature of reactioncalcium-cyanainid formed from sintering in th zone of'reaction proper onaccount'of,

the*heatdeveloped during the reaction after the beginning-thereof. c Theobject of -theipresent invention is to overcome the said-drawbacks inusing rotary tube furnacesiffor the manufacture of calciumjcyanamid,iThe invention consists mainly in this,

that the furnace is provided with means for f I H end thereof. ;The inecting nozzles may,

maintaining acontinuous circulation. of the :and on the other -side,- inpreventing the nitrogen contained in the furnace in op'posite directionto the solid material passing through the same. As return passages therei ai'e',-pi'efe1'ably, used channels provided in thewalls-of the furnaceor a central channel in such manner that thetubefurnace forms a closed"system of circulation with.- out tllilgfitltef conduits' As *dri-vi'ngagent for said circulation the nitrogen itself 'supplied under pressureis used. Owingi to the insignificant resistance .to the circulation ofthe gases. the nitrogen supplied will be capable of keeping a many timeslarger quantit'v of gas in circulation, whereby a uniform distributionof the heat of the zone of reaction is attained, and the heat of thefinished material as well as the excess of heat gitudinal section of'arot-arytube furnace according to my present invention.

Referring to the drawing, the 'main 'part of the furnace consists, inwell known manner, of a tube 2 resting on ball or rollerbearings l andprovided with adriving device ofany toward the inlet end of the furnacein Order e freshly introduced carbid to i kindito'rotate the tube aboutits longitudinal'anis. ;\s is usual in rotary furnaces, the tubennclmessomewhat,toward the outlet end 111 order to effect automatic feeding ofthe material through the furnace.

4 is a stationaryfeeding hopper for the carbid being provided at thebottom with a feeding screw 5 01' any otlier'suitable device for feedingthe carbid into the furnace. The mantle ofi'the feeding .screwiisprovided with-double walls and forms a chainbet 6 for distribution ofthe nitrogen which is supphedainder pressure through a conduit ftThefeeding screw and its mantle pass centrally through the end wall 21of" the tube furnace in such manner that the necessary tightening isefiected without interfering with the rotation of v the furnace. Fromthe distribi'ition chamber, 6 a number of injectin'g'nozzles 8' extendsinto a chamber 9 provided at the in'letend of the furnace and connectedatthe one side with the main channellOof the furnace through apertures,11 andat the other sidewith longitudinalchannel 12 arranged in. themantle of the furnace and leading to the other preferably,ibe surroundedby conical guidingwallsin order to increase the nectmgactionfexert'ed'upon the nitrogen contained in may decrease towardthe ends. The furnace is then filled up with nitrogen and rotated, andat the same time the feeding of calcium carbid through the screw.commences. The introduced carbid moves, owing to the rotation of thefurnace and its inclined position, forward through the furnace and isheated to the temperature of reaction. The principal reaction isperformed at the hottest middle partof the furnace. As soon as thereaction has commenced, the supply of nitrogen is started and is,preferably,- so regulated that a certainoverpressure is maintained inthe furnace to prevent the air from entering. The nitrogen suppliedunder high pressure and injecting through the nozzles S entrains thenitrogen contained in the furnace causingit to circulate through thechamber 9, the channels 12, the chamber 13, the collecting chamber 15and the main channel 10 of the furnace. Owing to the insignificantresistance to this circulation of the gas it is possible, by means ofthe nitrogen supplied,to cause, without difficulty, a many times greaterquantity of nitrogen to circulate. This circulation is of very greatimportance for the performing of the reaction, since it renders aneffective utilization of the heat of thefinished material possible,regulates the temperature of the zone of reaction and effects thenecessary preheating of the freshly introduced material before it entersthe-zone of reaction. The heat developed during the reaction will,generally, be suiiicient to maintain the necessary temperature in thezone of reaction. If, however, the heat developed during the reactionshould prove to be insufficient to maintain the temperature of thefurnace, the neces- 'sary quantity of heat is supplied electrically inany well known manner. ,2

' The invention 's not limited to the form of the tube furnace shown inthe drawing, but maybe modified in manyre'spects Without deviating fromthe principal features of the invention. Thus for lnstance the sup plyof nitrogen and the nozzles may be lo cated at-the outlet end of thefurnace, so

that the nozzles eject ajet of nitrogen, preferably with rotatingmovement,*directly into the outlet end of the tube furnace. To 0on ductthe, circulating nitrogen back to the outlet end of the furnace one'mayuse, at

At the starting themein channel 10 ofc furnace is heated, by blu'ning ofgas, as electrically in any well known manner, to a temperature of about1000 to 1300 C. at its middle part, While the temperature both ends withsaid main channel,- and in-- jecting nozzles supplying the nitrogen tothe furnace under pressure for causing the mtrogen contained in thefurnace to circulate through the longitudinal channels and the mainchannel and from the latter back tov the longitudinal channels,substantially as and for the purpose set orth.

2. Ina rotary tube furnace for producing calcium cyanamid from calciumcarbid and nitrogen, the combination of a central main channel passingalong the tubular furnace, a chamber arranged at each end of the furnaceand communicating with said. main channel,longitudinal channels locatedin the v: ll of the furnace and extending through the furnace, saidlongitudinal channels communicating at eachend with one of saidchambers, and injecting nozzles supplying the nitrogen under pressureinto one of said chambers and adapted to force the nitrogen through thelongitudinal channels and the main channel and from the latter backtothe longitudinal channels, substantially as and for the purpose setforth.

3. In a rotary tube furnace for performing a chemical reaction betweena-solid mass passing through the furnace and a gas contained in thefurnace, the combination ofa mam channel extending along the tubefurnace, longitudinal chanhels extending; through the furnace andcommunicating-at P both ends with said main channel, and means forsupplying gas under pressure to the furnac'e to produce a circulation ofthe gas con-- tained in the furnace through the longitudinal channelsandthe mainchannel and from the latter back to the longitudinalchannels.

In testimony that I claim theforegoing as my invention, I have signedmyname in presence of two subscribing'witnesses,

JOHAN HJALMAR LIDHOLM. Witnesses:

J. HonmsoN Harrier, MURRAY'A. UARsoN.

